1. Field of the Invention
The present invention relates to an arteriosclerosis evaluating apparatus for evaluating absence or presence, or degree, of arteriosclerosis of a superior-limb artery of a living subject. In the present application, the superior-limb artery is defined as encompassing a subclavian artery.
2. Related Art Statement
Atherosclerosis is a sort of arteriosclerosis and is characterized in that lipid, in particular, cholesterol deposits on the inner wall of artery and accordingly the arterial wall thickens. An artery suffering atherosclerosis has stenosis and its diameter reduces. Thus, atherosclerosis is also called arteriostenosis or arteriosclerosis obliterans. Calcification is another sort of arteriosclerosis and is characterized in that the media of artery hardens.
As a sort of device for inspecting arteriosclerosis, in particular, arteriostenosis, there is known an ankle-and-brachium-blood-pressure-index measuring device that inspects the stenosis by utilizing a fact that blood pressure lowers on a downstream side of a stenotic portion of an artery. Japanese Patent No. 3140007 or its corresponding U.S. Pat. No. 6,355,000 discloses an example of the index measuring device. The disclosed device includes two cuffs that are adapted to be worn on an ankle and a brachium of a living subject so as to measure an ankle blood pressure and a brachial blood pressure of the subject, respectively, then calculates an ankle-and-brachium blood-pressure index as a ratio between the ankle blood pressure and the brachial blood pressure, and finally evaluates presence or absence of arteriostenosis based on the thus calculated ankle-and-brachium blood-pressure index.
Generally, an ankle-and-brachium blood-pressure index is calculated as a proportion of an ankle systolic blood pressure to a brachial systolic blood pressure. In this case, if the thus calculated blood-pressure index is smaller than 0.9, that is, if the ankle systolic blood pressure is smaller than the product of the brachial systolic blood pressure and 0.9, it can be judged that the subject is suspected of arteriostenosis.
As another sort of device for evaluating arteriosclerosis, there is known a pulse-wave-propagation-velocity-related-information obtaining device that obtains pulse-wave-propagation-velocity-related information, such as pulse-wave propagation velocity or pulse-wave. propagation time, that is related to a velocity at which a pulse wave propagates between two portions of a living subject. Japanese Patent Laid-Open Publication No. 8-257002 or its corresponding U.S. Pat. No. 5,743,856 discloses an example of the information obtaining device. Since pulse-wave-velocity-related information is influenced by calcification or arteriostenosis, the information can be used to evaluate arteriosclerosis. For example, pulse-wave propagation velocity as a sort of pulse-wave-velocity-related information is influenced by arteriosclerosis, such that the velocity increases as calcification advances, and decreases as the degree of arteriostenosis increases.
In many cases arteriostenosis occurs to an inferior-limb artery, but in some cases it occurs to a superior-limb artery. For example, it is known that the stenosis occurs to a subclavian artery. However, as described above, ankle-and-brachium blood-pressure index is calculated as the proportion of ankle blood pressure to brachial blood pressure. That is, whether the ankle blood pressure is abnormal is judged by comparing the ankle blood pressure with the brachial blood pressure. Therefore, based on the ankle-and-brachium blood-pressure index, it can be judged whether an artery between the heart and the ankle, in particular, an inferior-limb artery has stenosis. However, it is difficult to judge, based on the ankle-and-brachium blood-pressure index, whether a superior-limb artery has stenosis.
Hence, the Inventors propose, in a related application, an arteriostenosis inspecting apparatus that inspects arteriostenosis of a superior limb based on a left-and-right-superior-limb-blood-pressure ratio as a ratio between a left-superior-limb blood pressure and a right-superior-limb blood pressure. If an artery of a left or right superior limb suffers stenosis, blood pressure in the stenotic artery lowers. Therefore, a left-and-right-superior-limb-blood-pressure ratio obtained in the case where neither of the left and right superior limbs has arteriostenosis, differs from that obtained in the case where only one of the two superior limbs has the stenosis. Thus, based on the left-and-right-superior-limb-blood-pressure ratio, it can be judged whether a superior-limb artery has arteriostenosis.
However, in the case where an artery of a left or right superior limb has stenosis, the stenotic artery may simultaneously suffer advanced calcification. In this case, the stenosis may be overlooked by the inspection based on only the left-and-right-superior-limb-blood-pressure ratio. More specifically described, if an artery has stenosis, blood pressure should lower, because of the presence of the stenosis, on a downstream side of the stenotic portion of the artery. If, however, calcification occurs to the downstream-side portion of the artery where a cuff is worn, the blood pressure should increase because an additional pressure is needed to press or widen the hardened portion of the artery. Thus, if the blood-pressure increase caused by the calcification of the artery is equal to, or greater than, the blood-pressure decrease caused by the stenosis of the artery, the superior-limb blood pressure should apparently take a normal value and accordingly the left-and-right-superior-limb-blood-pressure ratio should apparently take a normal value.
In addition, as described above, pulse-wave propagation velocity increases as calcification advances, and decreases as the degree of arteriostenosis increases. That is, arteriostenosis and calcification influence pulse-wave propagation velocity in different manners. Therefore, if arteriostenosis and calcification simultaneously occur, pulse-wave propagation velocity may apparently take a normal value.
It is therefore an object of the present invention to provide an arteriosclerosis evaluating apparatus which can accurately evaluate degree of arteriosclerosis of a superior limb of a living subject.
The above object has been achieved by the present invention. According to the present invention, there is provided an arteriosclerosis evaluating apparatus, comprising a left-superior-limb-blood-pressure measuring device which measures, with a cuff, a left-superior-limb blood pressure of a left superior limb of a living subject; a right-superior-limb-blood-pressure measuring device which measures, with a cuff, a right-superior-limb blood pressure of a right superior limb of the subject; a left-and-right-superior-limb-blood-pressure-ratio determining means for determining a left-and-right-superior-limb blood-pressure ratio as a ratio between the left-superior-limb blood pressure measured by the left-superior-limb-blood-pressure measuring device and the right-superior-limb blood pressure measured by the right-superior-limb-blood-pressure measuring device; a pulse-wave-propagation-velocity-related-information obtaining device which obtains at least one set of pulse-wave-propagation-velocity-related information that is related to at least one velocity at which at least one pulse wave propagates in at least one of (a) a first body portion of the subject that includes at least a portion of the left superior limb and (b) a second body portion of the subject that includes at least a portion of the right superior limb; and a display device which displays the left-and-right-superior-limb blood-pressure ratio determined by the left-and-right-superior-limb-blood-pressure-ratio determining means, and the at least one set of pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device, such that the left-and-right-superior-limb blood-pressure ratio and the at least one set of pulse-wave-propagation-velocity-related information are comparable with each other by a person.
According to this invention, the left-and-right-superior-limb blood-pressure ratio is determined, and the at least one set of pulse-wave-propagation-velocity-related information is obtained from the at least one of (a) the first body portion of the subject that includes at least the portion of the left superior limb and (b) the second body portion of the subject that includes at least the portion of the right superior limb. In addition, the left-and-right-superior-limb blood-pressure ratio and the pulse-wave-propagation-velocity-related information are displayed by the display device, such that the left-and-right-superior-limb blood-pressure ratio and the pulse-wave-propagation-velocity-related information are comparable with each other by a person. Therefore, based on the comparison of the left-and-right-superior-limb blood-pressure ratio and the pulse-wave-propagation-velocity-related information with each other, the person can judge as follows: Even if the left-and-right-superior-limb blood-pressure ratio may not indicate the presence of arteriostenosis, but if the pulse-wave-propagation-velocity-related information indicates the presence of advanced calcification, then the person can judge that the blood-pressure decrease caused by the stenosis is offset by the blood-pressure increase by the calcification and accordingly the left-and-right-superior-limb blood-pressure ratio takes the apparently normal value, and therefore that the subject may suffer the stenosis. In addition, even if the pulse-wave-propagation-velocity-related information may fall in a normal range, but if the left-and-right-superior-limb blood-pressure ratio indicates the stenosis, then the person can judge that the change of pulse-wave-propagation-velocity-related information caused by the calcification is offset by the change of the information caused by the stenosis and accordingly the information takes the apparently normal value, and therefore that the subject may suffer the calcification.
Here, preferably, the pulse-wave-propagation-velocity-related-information obtaining device obtains the at least one set of pulse-wave-propagation-velocity-related information from the at least one of (a) the first body portion of the subject that includes at least the portion of the left superior limb and does not include the right superior limb and (b) the second body portion of the subject that includes at least the portion of the right superior limb and does not include the left superior limb. According to this feature, a set of pulse-wave-propagation-velocity-related information is influenced by arteriosclerosis of only one superior limb but is not influenced by arteriosclerosis of the other superior limb. Therefore, the person can accurately judge whether a portion of the one superior limb where a blood pressure is measured suffers calcification and, in the case where the left-and-right-superior-limb blood-pressure ratio indicates normalcy, the person can accurately judge whether the normalcy is because there is no arteriostenosis or because there are not only arteriosclerosis but also calcification.
Also, preferably, the pulse-wave-propagation-velocity-related-information obtaining device obtains the at least one set of pulse-wave-propagation-velocity-related information from the at least one of (a) the first body portion of the subject that includes at least the portion of the left superior limb where the left-superior-limb blood pressure is measured and (b) the second body portion of the subject that includes at least the portion of the right superior limb where the right-superior-limb blood pressure is measured. According to this feature, the person can accurately judge, based on a set of pulse-wave-propagation-velocity-related information, whether an arterial wall of a portion of a superior limb where a blood pressure is measured suffers calcification. Therefore, in the case where the left-and-right-superior-limb blood-pressure ratio indicates normalcy, the person can accurately judge whether the normalcy is because there is no arteriostenosis or because there are not only arteriosclerosis but also calcification.
Also, preferably, the pulse-wave-propagation-velocity-related-information obtaining device obtains a set of pulse-wave-propagation-velocity-related information from each one of (a) the first body portion of the subject that includes at least the portion of the left superior limb and does not include the right superior limb and (b) the second body portion of the subject that includes at least the portion of the right superior limb and does not include the left superior limb. According to this feature, each of the two sets of pulse-wave-propagation-velocity-related information is influenced by arteriosclerosis of only a corresponding one of the left and right superior limbs but is not influenced by arteriosclerosis of the other superior limb. Therefore, the person can accurately judge, based on each of the two sets of pulse-wave-propagation-velocity-related information, whether a portion of the corresponding one superior limb where a blood pressure is measured suffers calcification and, in the case where the left-and-right-superior-limb blood-pressure ratio indicates normalcy, the person can accurately judge whether the normalcy is because there is no arteriostenosis or because there are not only arteriosclerosis but also calcification.
Also, preferably, the pulse-wave-propagation-velocity-related-information obtaining device obtains the set of pulse-wave-propagation-velocity-related information from the each one of (a) the first body portion of the subject that includes at least the portion of the left superior limb where the left-superior-limb blood pressure is measured and (b) the second body portion of the subject that includes at least the portion of the right superior limb where the right-superior-limb blood pressure is measured. According to this feature, the person can accurately judge, based on each of the two sets of pulse-wave-propagation-velocity-related information, whether a portion of a corresponding one of the left and right superior limbs where a blood pressure is measured suffers calcification and, in the case where the left-and-right-superior-limb blood-pressure ratio indicates normalcy, the person can accurately judge whether the normalcy is because there is no arteriostenosis or because there are not only arteriosclerosis but also calcification.